perf: add bounding box pre-check before Path.IsVisible in hover detection

Path.IsVisible was consuming 52% of CPU on mouse move. Add a cheap
GetBounds().Contains() check first so only parts under the cursor
hit the expensive GDI+ path test.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest/Controls/PlateView.cs

@@ -355,7 +355,8 @@ namespace OpenNest.Controls
                 LayoutPart hitPart = null;
                 for (var i = parts.Count - 1; i >= 0; --i)
                 {
-                    if (parts[i].Path.IsVisible(graphPt))
+                    if (parts[i].Path.GetBounds().Contains(graphPt) &&
+                        parts[i].Path.IsVisible(graphPt))
                     {
                         hitPart = parts[i];
                         break;